The present invention relates to dual propeller drive systems and more particularly a device for converting a single drive shaft to a multi-propeller drive system.
It should be clearly understood that while the present invention is described with respect to a dual propeller drive system for a marine vehicle, the propulsion system of the present invention can be used upon and relates to propulsion systems for land as well as marine vehicles, such as tractors, military tanks and farm tractors having controllable power applied to each of the driven arrangements such as the treads of the land vehicles mentioned hereinabove.
As is well known in the art, dual propeller systems provide for greater maneuverability and for greater directional stability against wind and water currents than do single propeller drive systems. Increased maneuverability and directional stability make navigation through crowded waters easier and facilitates docking of a marine vehicle. Dual propeller drive systems obtain this greater maneuverability and directional stability by individually controlling propeller speed in such a manner as to allow the propellers to rotate at different speeds. The rotating propellers at different speeds enable the marine vehicle to change its course without having to change the position of the propellers or the position of a rudder.
While various conventional arrangements have been developed to obtain the benefit of individually controllable propeller speeds, such arrangements generally suffer from one or more disadvantages. For example, some of these arrangements use a separate engine and transmission system for each propeller. This generally increases the size, weight and expense of the system and requires a corresponding increase in the amount of time and expense required to maintain and operate such system. Other arrangements, such as that disclosed in U.S. Pat. No. 3,112,728, uses a single engine with a separate transmission system for each propeller. However, such dual transmission arrangements suffer from the added size, expense and required maintenance associated with a second transmission system.
A dual propeller drive system using a single transmission is described in U.S. Pat. No. 3,922,997. However, the single transmission system of this patent requires separate gear sets, clutch assemblies and associated control elements for each propeller drive shaft. The use of separate gear sets, clutches and control elements generally increases the size, expense, complexity and/or required maintenance of the propeller drive systems.
None of the above mentioned systems implement a multi-propeller drive system that allows the speed of each propeller to be independently controlled without using relatively expensive and complex equipment, or a separate engine and transmission system for each propeller.
U.S. Pat. No. 5,413,512, discloses a multi-propeller drive system having a single input shaft for connection to an engine system, a differential gear assembly for dividing the driving force from the input drive shaft between a pair of output shafts and a pair of laterally spaced propellers driven by the output shafts of the differential gear assembly. The differential gear assembly operates in a manner wherein one output shaft, if required, is permitted to revolve at a different rate than the other output shaft. A pair of brake mechanisms acting on the output shafts of the differential gear assembly enable an operator to control the rotational speed of the respective propellers without modifying the engine speed or the transmission setting. The control associated with the drive system of this patent enables the control of the rotational speed of the propellers from a zero value to a positive value, but does not enable control of the propeller speed from a zero value to a negative value thereby controlling the direction of rotation of the dual propellers. Also, the arrangement of this prior art patent has a disadvantage due to difficulty in maintaining balance of speeds at the propellers.
The propulsion system of the above mentioned patents with the exception of U.S. Pat. No. 5,413,512 have a number of disadvantages, namely, the space required for a dual engine installation in a marine vehicle; the high operating costs due to the fuel flow requirements associated with two engines; the reduction in fuel tank capacity, and thus operating range, due to overall space limitations; the initial cost and maintenance of dual engines; and the general complication of operating four independent controls (speed and direction of each engine) in order to accomplish the desired maneuvering of the vehicle.